Multifunctional Metal Nanoparticles Having A Polydopamine-Based Surface and Methods of Making and Using the Same

ABSTRACT

The present invention provides nanoparticles including a metallic core having a length along each axis of from 1 to 100 nanometers and a coating disposed on at least part of the surface of the metallic core, wherein the coating comprises polydopamine, along with methods for making and using such nanoparticles. The metallic core may be gold, silver or iron oxide and the polydopamine coating may have other substances bound to it, such as silver, targeting ligands or antibodies, or other therapeutic or imaging contrast agents. The disclosed nanoparticles can be targeted to cells for treating cancer or bacterial infections, and for use in diagnostic imaging.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/420,189, filed Mar. 14, 2012 and claims the benefit of U.S.Provisional Application No. 61/453,054, filed on Mar. 15, 2011, both ofwhich are incorporated by reference herein in their entirety for allpurposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Grant Numbers R43DE014193, F31 DE019750, and R01 EB005772-01 A2 awarded by the NationalInstitutes of Health. The government has certain rights in theinvention.

FIELD OF THE INVENTION

This disclosure relates generally to metal nanoparticles that aresurface-coated with polydopamine. In addition, the disclosureencompasses methods of making such nanoparticles and methods for usingsuch nanoparticles in medical diagnosis and treatment.

BACKGROUND OF THE INVENTION

Metal nanoparticles (NPs) have a long history of use dating back to the4^(th) or 5^(th) century B.C.E. The optical properties of conductivegold and silver NPs have been associated with the surface plasmonresonance (SPR) of metals, which when confined to small colloids, isreferred to as the localized surface plasmon resonance (LSPR). Thisphenomenon, in which the free electrons oscillate collectively on themetal surface when irradiated with particular energies of light, causeswavelength dependent absorption and scattering of light and is thesource of the colors associated with metal nanoparticles. The size,shape, and composition of the colloidal particles determines the energyof the SPRs, and therefore, control over the synthesis of metal NPsprovides an ability to tune the optical properties of the nanometalscontained therein.

Since Turkevich et al. first described the synthesis of metalnanoparticles by reduction of cationic noble metal ions in solution(Discuss. Faraday Soc. 11 (1951): 55), colloidal suspensions of variousNP morphologies have been accomplished, including gold-silver alloys (Y.Sun et al., Analyst 128 (2003): 686-691), core-shell NPs (D. B. Wolfe etal., Langmiur 15 (1999): 2745), gold nanorods (NRs) (N. R. Jana et al.,J. Phys. Chem. B 105(19) (2001): 4065-4067), silver nanosheets (J. Xieet al., ACS nano 1(5) (2008): 429-439, and gold nanocages (J. Chen etal., Nano Lett. 5(3) (2005): 473-477). Hybrid approaches such assilver-shell gold NR core NPs have also been employed (M. Lui et al., J.Phys. Chem. B 108 (2004): 5882-5888).

Surface plasmon resonant metal nanoparticles have broad potential inmedical diagnostic and therapeutic applications, due to their relativeinertness, sub-100 nm size, unique electromagnetic properties, andstrong optical tunability. Accordingly, metal NPs have attractedattention in the biomedical field. For example, linking DNA to gold NPsallows biological interactions to form assemblies of colloidal clustersthat change the optical properties of the suspension (C. A. Mirkin etal., Nature 382 (1996): 607-609), which can be detected for diagnosticpurposes. Because SPRs enhance many optical processes, including Ramanscattering, fluorescence, and two-photon excited luminescence, gold NPshave been used in optical diagnostics (K. Asian et al., Current Opinionin Chemical Biology 9 (2005): 538-544) and as contrast agents forbioimaging (I. H. El-Sayed et al., Nano Letters 5(5) (2005): 829-834; K.C. Black et al., Mol. Imaging 7(1) (2008): 50-57). When gold NPs absorblight energy, they also release heat, potentially making them useful inphotothermal therapy applications targeting cancer (T. B. Huff et al,Nanomedicine 2(1) (2007): 125-132) and bacterial cells (S. E. Norman etal., Nano letters 8(1) (2008): 302-306.

However, the use of metal NPs for medical diagnosis and treatment islimited, because NPs cannot be fully integrated into the biologicalrealm without tailored control over their surface chemistry.Biomolecules and cells interact through a multitude of chemicalinteractions and physical forces which have not evolved in the presenceof noble metals, and therefore interactions between biological systemsand metal NPs are non-specific. In order to realize the full biomedicalpotential of gold nanoparticles, the nanoparticles must interactspecifically with biological matter, including cell surface components.Furthermore, nanoparticle aggregation and nonspecific interactions withmolecular and cellular constituents of the biological system must beminimized. Thus, there is a need in the art for metal nanoparticles thatcan be readily modified to precisely control their electromagnetic andbiofunctional properties.

SUMMARY OF THE INVENTION

The disclosure encompasses novel metal nanoparticles having polydopaminepolymerized onto the nanoparticle surface. In some embodiments, thesurface is modified further in a variety of ways. Non-limiting examplesof the function of such further modifications include modulatingtoxicity, controlling the conversion of light energy to heat energy,inhibiting non-specific interactions, increasing solubility inphysiological conditions, providing pro-apoptotic function, providingspecific targeting, and providing growth factor pathway inhibition.

Accordingly, in a first aspect, the disclosure encompasses nanoparticlesthat includes a metallic core having a length along each axis of from 1to 100 nanometers, and a polydopamine coating disposed on at least partof the surface of the metallic core. In some embodiments, the metalliccore is a nanorod having a substantially cylindrical shape. In someembodiments, the polydopamine coating is disposed on the entire surfaceof the metallic core. In some embodiments, the metallic core includesgold, and optionally, may consist essentially of gold.

The polydopamine coating may be modified in a number of ways, dependingon the desired function of the nanoparticles. For example, in someembodiments the coating may further include silver. In some embodiments,the coating may further include iron oxide. In some embodiments, thenanoparticles further include one or more polymers, polysaccharides,sugar-containing peptoids, pharmaceutical agents, antibodies,polyethylene glycol, or a functionalized polyethylene glycol bound tothe coating. Optionally, one or more of the bound antibodies is ananti-cancer cell surface receptor antibody or an anti-bacterial surfaceantibody. Optionally, one or more of the bound pharmaceutical agents isan anti-cancer agent or an anti-microbial agent.

In a second aspect, the disclosure encompasses a method of making thenanoparticles described above. The method includes the step ofcontacting a metallic core having a length along each axis of from 1 to100 nanometers with an alkaline solution comprising dopamine. This stepresults in the formation of a polydopamine coating on the surface of themetallic core. In some embodiments, the metallic core is a nanorodhaving a substantially cylindrical shape. In some embodiments, themetallic core consists essentially of gold.

In a third aspect, the disclosure encompasses a method for treatingcancer. The method includes the step of administering to a patienthaving cancer cells one or more of the nanoparticles that are describedabove. In some embodiments, the metallic core consists essentially ofgold, and one or more anti-cancer cell surface receptor antibodies arebound to the polydopamine coating of the nanoparticles. The antibodiescause the nanoparticles to target the cancer cells. A non-limitingexample of an antibody that could be bound to the coating of thenanoparticles to target cancer cells is an anti-epithelial growth factorreceptor (EGFR) antibody.

In some embodiments, the nanoparticles may further include an additionalanti-cancer agent bound to the polydopamine coating. A non-limitingexample of such an anti-cancer agent is a proteasome inhibitor, such asbortezomib.

In some embodiments, the method further includes the step of exposingthe nanoparticles to light. Upon such exposure, the nanoparticles heatup, and the resulting photothermal therapy differentially kills thetargeted cells.

In a fourth aspect, the disclosure encompasses a method for treating abacterial infection. The method includes the step of administering to apatient infected with bacteria one or more of the nanoparticlesdescribed above that include a metallic core consisting essentially ofgold and an anti-bacterial surface antibody bound to the polydopaminecoating. The nanoparticles then target the bacteria that is the sourceof the infection.

Optionally, the anti-bacterial surface antibody is an anti-lipoteichoicacid antibody or an anti-endotoxin antibody. In some embodiments, thepolydopamine coating further incorporates a layer of silver. In someembodiments, the method further includes the step of exposing thenanoparticles to light.

In a fifth aspect, the disclosure encompasses a method for imagingcancer or bacterial cells. The method includes the steps of contactingcancer or bacterial cells with one or more of the nanoparticlesdescribed above, wherein the metallic core consists essentially of goldand wherein the nanoparticles include an anti-cancer cell surfacereceptor antibody or an anti-bacterial surface antibody bound to thepolydopamine coating. The antibody functions as a targeting agent sothat the nanoparticles target the cancer or bacterial cells.

The method also includes the step of detecting the location of the oneor more nanoparticles. Optionally, this step may be performed usingbright field microscopy, optical coherence tomography, or 2-photonconfocal microscopy. In some embodiments, the nanoparticle coatingfurther comprises iron oxide, and the step of detecting the location ofthe one or more nanoparticles is performed using magnetic-based imaging.

Further objects, features and advantages of the invention will beapparent from the following detailed description when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing UV-Vis extinction for three different nanorodsuspensions.

FIG. 2 is a graph showing the results of optical extinction spectroscopyof polydopamine (PD)-coated gold NRs after the addition of silver.

FIG. 3 shows polydopamine-coated gold nanorods (NRs) conjugated to ironoxide nanoparticles (FIGS. 3a and b ). FIG. 3(c) shows the movement ofthe these conjugates with an external magnet, and FIG. 3(d) shows theiroptical spectrum in suspension after movement with the magnet andsubsequent resuspension.

FIG. 4 is a graph showing the results of optical extinction spectroscopyof polydopamine (PD)-coated gold NRs with the addition of differentpolyethylene glycols (PEGs).

FIG. 5 is an EM image in the secondary electron mode of PD-coated NRsafter conjugation with methoxypolyethylene glycol (mPEG).

FIG. 6 is a graph showing the results of optical extinction spectroscopyof cetyl trimethylammonium bromide (CTAB)-coated NRs andpegylated-PD-coated NRs. Notice the red-shift after exchanging CTAB withPD.

FIG. 7 shows the use of gold nanorods conjugated to iron oxidenanoparticles for cancer therapy: MDA-MB-231 breast cancer cellviability after treatment with gold NR-IONP conjugates and lightirradiation, (a) without and (b) with the use of a magnet to attract theconjugates to cells. FIG. 7(c) shows quantitative cell viabilitydetermined from cell images.

FIG. 8 is a schematic of the optical coherence tomography (OCT) systemused for cellular imaging. M=mirror, DC=dispersion compensation, BS=beamsplitter, Galvo=galvo mirror, G=holographic diffraction grating,CCD=line scan camera, GRB=frame grabber, FG1,2=function generators,SS=sample stage, DAQ=data acquisition computer.

FIG. 9 shows quantification of IgG antibody density on gold nanorod (NR)surface. (a) Ratio of the concentration of antibody immobilized on goldNR surface compared to the concentration of unbound antibody insolution. FIG. 9(b) Antibody density as a function of concentration ofantibody added to 3.62×10¹³ NR/L.

FIG. 10 is a schematic illustration of the preparation of EGFRantibody-conjugated gold NRs (Anti-EGFR-PD-NRs) using a polydopamine‘primer’ coating.

FIG. 11 is a TEM image of cetyl trimethylammonium bromide (CTAB)stabilized gold nanorods.

FIG. 12 shows (a) optical extinction spectroscopy of gold NRs stabilizedwith cetyltrimethylammonium bromide (CTAB) before and after reactionwith 555 μM dopamine in pH 8.5 for 30 minutes, (b) Secondary electronmicroscopy of gold NRs coated in polydopamine (PD-NRs).

FIG. 13 shows the results of X-Ray photoelectron spectroscopy of gold NRsamples on silicon surfaces. FIG. 13 (a) shows survey scans and FIG. 13(b) shows high resolution C1s scans of (top) CTAB-NRs and (bottom)PD-NRs.

FIG. 14 shows anti-EGFR antibody immobilization onto polydopamine-coatedNRs (PD-NRs). (a) UV-Vis extinction of PD-NRs before and after anti-EGFRantibody conjugation ([NR]=0.0150 nM); (b) Stability of longitudinalplasmons of PD-NRs functionalized with anti-EGFR antibodies inserum-containing DMEM.

FIG. 15 shows optical imaging of cells incubated with NRs. Bright fieldlight microscopy images of OSCC15 oral cancer cells incubated with (a)PEG-PD-NRs, and (b) anti-EGFR-PD-NRs. Scale bars in a and b=20 μm. (c)OCT intensity from individual MDA-MB-231 breast cancer cells as afunction of anti-EGFR-PD-NR concentration.

FIG. 16 shows cell images resulting from photothermal therapy of OSCC15cells. Images of cells treated as follows: (a) cells irradiated for 5minutes in the absence of NRs; (b) cells incubated for 1.5 hours with9.92 pM anti-EGFR-PD-NRs with no irradiation; (c) cells incubated for1.5 hours with 9.92 pM PEG-PD-NRs and irradiated for 5 minutes, (d)cells treated with 9.92 pM anti-EGFR-PD-NRs and irradiated for 5minutes.

FIG. 17 shows viability data for OSCC15 and MDA-MD231 cells treated withNRs followed by photoirradiation. (a) viability of OSCC15 cells after notreatment (control), irradiation for 5 minutes in the absence of NRs,irradiation for 5 minutes after incubation with PEG NRs ([NR]=9.92 pM),and irradiation for 5 minutes after incubation with anti-EGFR-PD-NRs([antibody]=4.0 nM; [NR]=9.92 pM); (b) dependence of MDA-MB231 cellviability on anti-EGFR-PD-NR concentration after incubation withanti-EGFR-PD-NRs for 1 hour followed by 5 minutes of irradiation; (c)dependence of MDA-MB231 cell viability on incubation time withanti-EGFR-PD-NRs ([NR]=3.0 pM). Viability was measured (a) 30 minutes or(b,c) 19 hours after a 5 minute irradiation treatment.

FIG. 18 is a schematic diagram representing the polydopamine-basedstrategy to form multifunctional antibacterial metal nanorods.

FIG. 19 is a schematic diagram representing the formation of the nanorodformulations described and used in this study.

FIG. 20 shows polydopamine (PD) polymerization onto gold NR. (a)Red-shift in the longitudinal surface plasmon resonance of the gold NRsduring reaction in 520 μM dopamine in pH 8.5; (b) Secondary electronmicroscopy of PD-coated NRs (scale bar=80 nm).

FIG. 21 shows the optical properties of polydopamine-coated gold NRs(PD-NRs) upon silver addition. (a) photos of PD-NR suspensions afteraddition of (from right to left) 0 μM, 50 μM, 100 μM, 200 μM, 300 μMAgNO₃; (b) Optical extinction spectroscopy of PD-NRs after addition ofAgNO₃, and (c) Optical extinction and backscattering from an individualNR sample after addition of silver.

FIG. 22 shows (a) transmission electron microscopy (TEM) image, and (b)Z-contrast electron microscopy (ZCEM) image of poydopamine-coated goldnanorods with silver deposition (PEG-Ag-NRs).

FIG. 23 shows energy dispersive x-ray spectroscopy (EDS) spectralimaging of polydopamine coated NRs (PD-NRs) after addition of 0 μM(top), 100 μM (middle), and 300 μM (bottom) AgNO₃: (a, f, k) Z-contrastelectron microscopy (ZCEM) image; (b, g, I) silver EDS image; (c, h, m)gold EDS image; (d, i, n) merged image; (e, j, o) optical extinctionfrom respective NR suspensions with color photo of suspensions (inset).Scale bar=20 nm.

FIG. 24 shows quantification of silver atoms per gold nanorod withinductively-coupled plasma optical emission spectroscopy (ICP-OES).

FIG. 25 shows X-ray photoelectron spectroscopy (XPS) of Ag 3d peaks frompolydopamine-coated nanorods (PD-NRs) after addition of (a) 0 μM, (b)160 μM AgNO₃.

FIG. 26 shows heating profiles of NR suspensions upon irradiation withlight.

FIG. 27 shows antibody-functionalized metal nanorod (NR) stability in0.85% salt. (a) Optical extinction spectra of antibody functionalizedNRs (Ab-NRs and Ab-Ag-NRs), and (b) shift in the center wavelength ofthe longitudinal surface plasmon resonance of NRs in 0.85% over time.

FIG. 28 shows optical coherence tomography (OCT) images of E. coli(left) and S. epidermidis (right). Images of cell pellets alone (top),pellets incubated with PEG-functionalized nanorods (PEG-NRs, middle),and pellets incubated with NRs functionalized with silver and antibodies(Ab-Ag-NRs, bottom).

FIG. 29 shows optical coherence tomography (OCT) spectra from images of(a) S. epidermidis and (b) E. coli seen in FIG. 28.

FIG. 30 shows S. Epidermidis toxicity after incubation with nanorods(NRs) and irradiation with light. (a) Fluorescent live/dead images and(b) quantitative viability determined from fluorescent images.

FIG. 31 shows E. Coli toxicity after incubation with nanorods (NRs) andirradiation with light. (a) Fluorescent live/dead images and (b)quantitative viability determined from fluorescent images.

FIG. 32 shows fluorescence images of (a) S. epidermidis and (b) E. colitreated with nanorods and light and stained with SYTO® 9 greenfluorescent nucleic acid stain and propidium iodide.

DETAILED DESCRIPTION OF THE INVENTION I. In General

Before the present materials and methods are described, it is understoodthat this invention is not limited to the particular methodology,protocols, materials, and reagents described, as these may vary. It isalso to be understood that the terminology used herein is for thepurpose of describing particular embodiments only, and is not intendedto limit the scope of the present invention which will be limited onlyby the appended claims.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural reference unless the context clearly dictatesotherwise. As well, the terms “a” (or “an”), “one or more” and “at leastone” can be used interchangeably herein. It is also to be noted that theterms “comprising”, “including”, and “having” can be usedinterchangeably.

Unless defined otherwise, all technical and scientific terms andabbreviations used herein have the same meanings as commonly understoodby one of ordinary skill in the art to which this invention belongs.Although any methods and materials similar or equivalent to thosedescribed herein can be used in the practice or testing of the presentinvention, the preferred methods and materials are now described. Allpublications and patents specifically mentioned herein are incorporatedby reference for all purposes including describing and disclosing thechemicals, instruments, statistical analysis and methodologies which arereported in the publications which might be used in connection with theinvention. All references cited in this specification are to be taken asindicative of the level of skill in the art. Nothing herein is to beconstrued as an admission that the invention is not entitled to antedatesuch disclosure by virtue of prior invention.

II. The Invention

Polydopamine (PD) has the ability to coat materials using mussel mimeticmechanisms, making it a versatile aqueous adhesive. The inventors reportherein the successful coating of metal nanoparticles, specifically goldnanorods, with polydopamine, by contacting the nanorods with an alkalinesolution containing dopamine. With the ability to coordinate to metals,π-stack, hydrogen bond, and covalently react through catechols, and tointeract electrostatically and react through amines, the polydopaminecoating provides a chemical repertoire to form evolutionary modulatorymetal nanoparticles.

The resulting multifunctional, multicomponent nanoparticles can be usedfor multimodal optical or magnetic imaging, such as in bright fieldmicroscopy, optical coherence tomography, 2-photon confocal microscopy,or for other targeted diagnostic imaging. The nanoparticles may also beused for photothermal therapy or for cancer, antimicrobial, or otherdrug delivery.

As outlined in more detail in the examples below, a conformal ‘primer’layer of polydopamine was first deposited onto surface plasmon resonantgold nanorods to form a versatile interface for biofunctionalization. Incertain embodiments, polyethylene glycol (PEG) polymers were covalentlyreacted to the biomimetic polydopamine layer to passivate the surface.In certain embodiments, antibodies were immobilized onto thepolydopamine-coated nanorods to provide bioactivity, and the number ofantibodies per nanoparticle was tuned to be between 8 and 400.

In certain embodiments where anti-cancer nanoparticles were formed,anti-EGFR antibodies were immobilized onto the polydopamine-coatednanorod surface, and the functionalized nanoparticles were found to bestable in serum-containing medium for 24 hours. In some suchembodiments, the antibody-functionalized nanorods bound specifically toEGFR-overexpressing oral and breast cancer cells, which were detected inboth bright field microscopy and optical coherence tomography. Incertain embodiments, targeted nanorods provided a strong synergistictherapeutic response with broad band light irradiation, causingsignificant death to EGFR-expressing cancer cells in vitro.

In certain embodiments where anti-bacterial nanoparticles were formed,anti-bacterial surface antibodies were immobilized onto thepolydopamine-coated nanorod surface. In some such embodiments, silverwas incorporated into the polydopamine coated nanorod surface. Theantibody-functionalized nanorods bound specifically to bacterial cells,and targeted nanorods provided a strong synergistic therapeutic responsewith broad band light irradiation, causing significant death tobacterial cells in vitro. This effect was especially pronounced fornanorods that included silver.

The versatile polydopamine surface modifications demonstrated herein canbe applied to functionalize nanoparticles composed of many materialswith a broad range of bioactive molecules, such as antibodies, peptides,and DNA aptamers for cancer treatment and other biomedical applications.With emerging advances in biotechnology such as high throughput geneticscreening, the polydopamine-coated nanoparticles have the adaptablechemical repertoire to facilitate the synthesis of individualized,multifunctional diagnostic and therapeutic agents for a broad range ofdiseases. The versatility of catechol chemistry allows the polydopaminesurface to be functionalized in a variety of ways, as demonstrated belowfor multimodal targeted imaging and synergistic therapy of cancer andbacterial infections.

Further, polydopamine itself is a photothermal modulatory material. Ithas a similar structure to that of melanin, a natural material used forphotoprotection by converting light energy into heat energy. Thereforepolydopamine coatings with tunable thicknesses on the nanorod allow forcontrol over the conversion of light energy to heat energy foroptimization of metal nanoparticles for optical contrast agents andphotothermal agents.

Accordingly, the disclosure encompasses nanoparticles that include ametallic core and a polydopamine coating disposed on at least part ofthe surface of the metallic core. As used herein, the term“nanoparticle” means a particle having a length along any axis passingthrough the center of the particle of from 1 to 100 nanometers. In someembodiments, the metallic core is a nanorod. As used herein, the term“nanorod” refers to a nanoparticle having a substantially cylindricalshape. In some such embodiments, the metal nanorod has a length of 1-100nanometers, 10-90 nanometers, 20-80 nanometers, 30-70 nanometers, or40-60 nanometers, and the metal nanorod has a width (diameter) of 1-50nanometers, 5-30 nanometers, or 10-20 nanometers. In some embodiments,the metallic core is made of gold.

Dopamine is a bifunctional catecholamine having the following chemicalstructure:

Under conditions typical of a marine environment (e.g., buffered to8.5), a dilute solution of dopamine can self-polymerize to formpolydopamine (H. Lee at al., Science 318(5849) (2007): 426-430). Themechanism likely involves oxidation of the catechol to a quinone,followed by polymerization in a manner reminiscent of melanin formation,which occurs through polymerization of structurally similar compounds.See scheme 1 below:

The inventors report herein the self-polymerization of dopamine to forma polydopamine coating onto the surface of metal nanoparticles,specifically onto the surface of gold nanorods. Once the polydopamine iscoated onto the metal surface, it may be modified in a number of ways,depending on the biological, optical, and/electromagnetic propertiesneeded to facilitate the desired function of the nanoparticles.

Metal NPs have SPR material properties that can be harnessed for avariety of biomedical applications when their surfaces arebiofunctionalized, including in the photothermal treatment of cancer orbacterial cells. Furthermore, the biomimetic strategy disclosed hereincan be expanded to include other functional nanomaterials likesuperparamagnetic iron oxide, and other targeting and therapeuticmoieties such as small molecule drugs and other cell-surface targetingantibodies, in order to form multifunctional agents for specificdiagnosis and combination therapy for complex resistant diseases such asheterogeneous cancers and antibiotic resistant bacteria.

The following examples are offered for illustrative purposes only, andare not intended to limit the scope of the present invention in any way.Indeed, various modifications of the invention in addition to thoseshown and described herein will become apparent to those skilled in theart from the foregoing description and the following examples and fallwithin the scope of the appended claims.

Example 1 Polydopamine-Based Assembly of Multifunctional,Multicomponent, Multimodal Metal Nanoparticles for SynergisticPhotothermal Mediated Diagnosis and Therapy

In this example, we describe the coating of a polydopamine (PD) layeronto the surface of gold nanorods. We further describe modifications tothe polydopamine surface of the nanorods in order to (1) immobilizesilver into the surface to tune the surface plasmon resonance and thetoxicity of the metal nanoparticles; (2) immobilize magnetic iron oxidenanoparticles into the layer to provide magnetic targetability; (3)react polyethylene glycol molecules into the layer with amine, thiol,catechol, and histidine functionalities to provide stealthcharacteristics, as well as provide proof of principle for diversefunctionalization chemistry mediated by catechol oxidation to quinine;(4) immobilize chitosan onto the gold nanorods to provide additionalmolecular functionality; (5) react sugar-containing peptoids withcatechol and amine containing anchors onto gold nanorods to providestealth properties; (6) react catechol-containingpoly-N-isopropylacrylamide (pNIPAM) onto the gold nanorod surface toprovide thermal and photothermal responsive solubility; (7) conjugateanti-EGFR antibodies onto the surface to provide specific EGFR targetingand inhibition; and (8) conjugate pro-apoptotic drugs into the layer toprovide pH dependent release of pro-apoptotic drugs.

Polydopamine (PD) was polymerized onto the surface of gold nanorods(NRs) to form a multifunctional, multicomponent anticancer surface.Specifically, silver was deposited into the PD layer to modulatetoxicity and tune the SPR throughout the visible and near-infraredportions of the electromagnetic spectrum. PEG was reacted into the PDlayer through Michael-type addition and Schiff base reactions to inhibitnon-specific interactions and increase solubility in physiologicalconditions. The proteasome inhibitor bortezomib was coordinated tocatechols in the PD layer to provide a pro-apototic effect, and theanti-EGFR antibody ERBITUX® (cetuximab) was reacted throughquinone-mediated cross-linking reactions to provide NPs with specifictargeting and growth factor pathway inhibition. NRs were identified onoral cancer cells with bright field microscopy, optical coherencetomography, and 2-photon excited confocal microscopy. Finally, targetedNR-mediated photothermal therapy was performed.

Importantly, the NPs provide multiple mechanisms of treatment, includingspecific targeting and inhibition of EGF pathways, toxicity from silver,pH-dependent release of bortezomib in acidic cancer microenvironments,and thermal heating to cause necrosis and permeabilize membranes toincrease drug uptake. Taken together, these catechol-based metalnanoparticles provide multimodal imaging and synergistic therapy forcancer.

Dopamine hydrochloride, Cetyltrimetylammonium bromide (CTAB, 99%),sodium tetrachloroaurate(III) dihydrate (NaAuCl₄.2H₂O, 99%), sodiumborohydride (NaBH₄, 98%), ascorbic acid, glycine, silver nitrate (AgNO₃,99%), and phosphotungstic acid (10% solution) were obtained fromSigma-Aldrich (St. Louis, Mo.). The pH value of the solution glycinesolution (0.2M) was adjusted with 2M sodium hydroxide to 8.0. PEG-SH(MW=5000) was purchased from Laysan Bio (Arab, Ala.). ERBITUX®(cetuximab) infusion was acquired from the Northwestern pharmacy(Chicago, Ill.). Ultrapure, deionized water (18.2 MΩ·cm) was used toprepare all of the aqueous solutions.

Synthesis of Gold Nanorods (NRs).

The synthesis of Au—Ag NRs was performed according to a slightlymodified method previously described in the literature. Briefly,cetyltrimethylammonium bromide (CTAB) aqueous solution (0.2 M, 5.0 mL,heated to 30° C.) was mixed with 0.5 mM of NaAuCl₄ (5.0 mL). Ice-cold0.01 M NaBH₄ (0.6 mL) was added to this solution and sonicated for 5minutes to form a brownish-yellow seed solution. Then 50.0 mL of 0.2 MCTAB were gently mixed with 50.0 mL of 1.0 mM NaAuCl₄ and 0.1 mL of 0.1M of silver nitrate to form a growth solution. Ascorbic acid was addedto the solution as a mild reagent (78.8 mM, 0.7 mL), followed byaddition of 120 μL of the seed solution. After 45 minutes, this Au NRseed solution was used directly to prepare the Au—Ag NRs. Simply, 100 mLof seed solution was mixed with 100 mL of 0.2 M glycine (pH 8.0). Thissolution was allowed to react overnight without stirring at ambienttemperature.

PD Polymerization onto Gold NRs.

1 mL of gold NR suspension was centrifuged and resuspended in 1.7 mL of10 mM TRIS or bicine buffer (pH 8.5). NRs were reacted in 258 μM-10.2 mMdopamine under sonication for 30 minutes-18 hours. 32-320 μM AgNO₃ wasadded under stirring to incorporate silver into the PD-layer. Topegylate the NRs, 0.2-3 mM mPEG-SH, mPEG-NH₂, mPEG-NH—Ac, and mPEG-H,and mPEG-C were added to solutions either simultaneously with or 30minutes-1 hour after dopamine addition. Bifunctional PEGs were alsoincorporated into the layers with the addition of biotin-PEG-dopaminepolymers. Similar experiments were performed with peptoid moleculescontaining DOPA-Lys anchor, poly N-isopropylacrylamide polymerscontaining catechol functionalities, and chitosan. Samples weresonicated for 2 additional hrs, rocked overnight, and UV-Vis-NIRspectrum was acquired. Samples were centrifuged at 9000 rpm for 15minutes; supernatant solution was removed. Pelleted NRs were resuspendedin 2 mL of ultrapure water, and another UV-Vis-NIR spectrum wasacquired. To perform experiments in salt, pelleted pegylated NRs wereresuspended in 100 mM sodium chloride, and monitored with opticalspectroscopy for 3 days.

Iron Oxide Nanoparticle Synthesis.

99.5 mg FeCl₂*4H₂O and 270.3 mg FeCl₃*6H₂O was dissolved in 30 mL waterand 605 μL 6N NaOH under slow stirring and reacted under Ar for 1.5hours. Particles were pelleted by magnet, supernatant was removed, andpellet was resuspended in ultrapure water.

Iron Oxide Nanoparticle Conjugation to Gold NR.

1 mL of gold NR suspension was centrifuged and resuspended in 1.7 mL of10 mM TRIS or bicine buffer (pH 8.5). NRs were reacted in 258 μMdopamine under sonication for 30 minutes and then centrifuged. Thesupernatant was discarded, the NRs were resuspended in 2 mL ultrapurewater, and 25 μL 2 mM stock iron oxide solution was added. The mixturewas sonicated for 2 hours, the conjugates were pelleted magnetically,and the clear supernatant was removed. A TEM grid was prepared, thepellet was resuspended in 1 mL ultrapure water, and UV-Vis spectra wereacquired.

Antibody Immobilization on Gold NRs.

1 mL of metal NR suspension was centrifuged at 9000 rpm and 23° C. for10 minutes, supernatant was removed, and the pellet was resuspended in1.7 mL of 10 mM TRIS buffer (pH 8.5). NRs were reacted in 516 μMdopamine under sonication for 30 minutes. To silverize the layer,6.5-65.5 μL of 10 mM AgNO₃ was added under stirring. 100 μL of 2 mg/mLERBITUX® (cetuximab) infusion added to the solution and sonicated for 30minutes. Samples were further centrifuged, supernatant was removed,pellets were resuspended in ultrapure water, and UV-Vis-near infrared(NIR) spectrum was acquired. To further confirm conjugation ofantibodies to gold NRs, 10-50 μL solution of antibodies labeled with 10nm gold NRs were incubated with PD-coated gold NRs, centrifuged, andimaged with electron microscopy.

Bortezomib Immobilization onto Gold NRs.

1 mL of metal NR suspension was centrifuged at 9000 rpm and 23° C. for10 minutes, supernatant was removed, and the pellet was resuspended in1.7 mL of 10 mM TRIS buffer (pH 8.5). NRs were reacted in 516 μMdopamine under sonication for 30 minutes. 1.2 mg bortezomib wasdissolved in 300 μL DMSO and added to the NR suspension which wassonicated for 30 minutes. 220 μM PEG-SH was added to the suspensionunder sonication for 30 minutes, and then suspensions were centrifugedand washed twice to remove excess dopamine and unbound bortezomib. Toconjugate ERBITUX® (cetuximab) and bortezomib to NRs, the same protocolwas followed, with PEG-SH replaced by 100 μL 2 mg/mL ERBITUX®(cetuximab) infusion.

Optical Spectroscopy.

A Hitachi (Hitachi City, Japan) U-2010 Spectrophotometer was used toacquire optical spectra in a two-beam geometry of samples. 10 mM TRISbuffer (pH 8.5) was used for the reference beam. Spectral scans wereperformed over the 200-1000 nm range of wavelengths in theUV-Visible-NIR region of the spectrum. A deuterium lamp was used for the200-340 nm UV range illumination and a halogen lamp was used for thevisible and NIR illumination. Spectral resolution was 1 nm.

Electron Microscopy (EM).

Pelleted NRs (54) were dropped on EM grids (Ted Pella, Redding, Calif.)and allowed to dry. To stain PEG, grids were immersed in 10%phosphotungstic acid solution for 90 seconds three times, and thenimmersed in pure water for 30 seconds. Transmission EM (TEM), Z-contrastEM, secondary EM (SEM), and energy dispersive X-ray spectroscopy (EDS)spectral imaging were performed on a Hitachi HD-2300 Ultra HighResolution FE-STEM (Hitachi City, Japan).

Multimodal Cellular Imaging.

Oral squamous cell carcinoma 15 (OSCC15) cells were grown in DMEMcontaining 10% FBS and 4% gentamycin. To image cells with NRs, 2 mL oftrypsin was added to confluent plates of OSCC15 cells, cells wereremoved, and 400 μL was added to 2 mL of DMEM high glucose media. Cellswere centrifuged at 1500 rpm for 5 minutes, supernatant was removed, and2 mL more media was added. NR suspensions from above were added to thecells and incubated for 30 minutes. Cells were centrifuged at 1500 rpmfor 5 minutes, supernatant was removed, 2 mL of media was added, andfinally cells were centrifuged and plated onto glass optical microscopyslides.

Bright field images were acquired in a Leica DMRX microscope.Additionally, optical coherence tomography (OCT) was acquired. A visibleband Fourier-domain OCT was used in this study. The system adopts acommonpath parallel configuration and the schematic is described in aprevious paper. The parallel configuration allowed simultaneous 2DB-scan OCT image acquisition (^(˜)1 mm cross and ^(˜)300 μm deep) with 5fps frame rate. 3-D images were obtained by scanning the sample stageacross the B-scan image plane. The axial resolution was ^(˜)1.5 μm givenby the bandwidth (540-650 nm), and the transverse resolution and depthof focus were ^(˜)6 μm and ^(˜)200 μm, respectively. 2-photon confocalmicroscopy was performed with a 40× oil immersion objective in anInverted Zeiss Axio Observer.Z1 Confocal Microscope. Differentialinterference contrast (DIC) images and 2-photon excited images wereacquired in two channels. A spectrum of the 2-photon emission between400 nm and 650 nm with 10 nm resolution was acquired in an Upright ZeissLSM 510 Confocal Microscope using the same Mai:Tai laser describedabove.

Photothermal Studies.

In addition, NRs were embedded in an alginate gel and imaged under arange of powers. Finally, suspensions of CTAB-coated and PD-coated NRswere irradiated with varying incident powers, and the 2-photon excitedvisible emission intensity was quantified.

Cellular Toxicity Experiments.

For long term toxicity experiments, NRs (0-95 μM Au) were incubated withOSCC cells in 6 and 12 well plates with 1 mL DMEM high glucose media for20-48 hours. 15 minutes before toxicity quantification, 1 μL 4 mMcalcein and 1 μL 4 mM ethedium bromide was added to each well, and cellswere incubated for 15 minutes. Fluorescence microscopy was performed ona Leica DM IRB light microscope and a QImaging QI Click camera. Red- andgreen-channel were acquired for each condition in triplicate, cells werecounted manually, and an average percent viable cell percentage wascalculated for each condition.

NP-Mediated Photothermal Therapy.

OSCC15 cells were cultured in 6-well plates. Cells were incubated withERBITUX® (cetuximab) conjugated NRs (62.5 μM Au) for 1 hour, and theneach well was irradiated with 50 mW NKT photonics SUPERK™ Versa lasersource for 5, 10, or 15 minutes. Spot size was 1 mm.

Magnetic Targeting and Photothermal Irradiation Experiments.

In the magnetic targeting experiments, 0-14 pM NR were added to 12 wellplates of MDA-MB-231 or MCF7 cells. A magnet was placed underneath thewells for 30 seconds, and then the cells were irradiated with the 50 mWVersaK source described in chapter 3 and 4. To quantify toxicity, 1 μLof 2 mM calcein and ethedium homodimer were added to each well andincubated for 15 minutes. Fluorescence microscopy was performed on aLeica DMIRB microscope, with a 250 W maximum Hg arclamp, and a QImagingQIClick detector. Calcein-stained and ethedium-homodimer stained cellswere counted, and % cell viability was quantified. Triplicate imageswere acquired for each condition.

Results.

Suspensions of CTAB-stabilized gold NRs were synthesized with apreviously reported protocol. Once formed, the apexes of the transverseand more intense longitudinal extinction peaks of CTAB-gold NRs werelocated between 515-530 nm and 756-872 nm, respectively, and were stableover the span of 6-12 months. Suspensions were imaged under TEM and hadan average length of 50±8 nm and width of 15±3 nm. To exchange the CTABcoating with a more functional PD layer, gold NR suspensions wereincubated in dopamine solution at pH 8.5. When NRs were mixed in 5.2 mMdopamine solutions and allowed to react overnight, brown to blackaggregates formed on the polystyrene tubes and in suspension, and theplasmon peaks from the NRs were permanently lost in the remaining liquidsample (FIG. 1). When NRs were mixed in 520 μM dopamine solutions andallowed to react overnight, a stable darkened suspension formed.

Silver was immobilized into the PD layer surrounding the NR. AgNO₃ (0 to320 μM) was added to the polymerizing suspension 30 minutes afteraddition of 516 μM dopamine. Suspension color changes occurred within 1minute of silver addition, which included red (no silver), orange (32μM), yellow (96 μM), green (160 μM), and blue (320 μM). Electronmicroscopy was performed on PD-coated NRs with and without the additionof silver nitrate. A homogeneous distribution of pure gold NRs (>95%)was evident in samples with no additional silver added. Under both TEmode and Z-contrast imaging, core-shell NRs were present in sampleswhere dopamine and silver were both added.

Coatings of tunable thickness ranging from 2.3 nm (32 μM) to 7.0 nm (320μM) were correlated with the color change. EDS spectral imagingconfirmed the presence of the silver coating around a gold NR. Thelongitudinal SPR peak of the NR sharpened and blue-shifted from 864 nminto the visible when coated with silver (FIG. 2). With a 7 nm thickcoating, the SPR shifted to 617 nm, with a 3.3 fold increase in theplasmon extinction intensity per particle. The SPR band width decreasedfrom 194 nm with no silver to a minimum of 118 nm with 164 μM silver.Only a very slight blue shift of 10 nm with no significant change in theline width occurred with the addition of silver in a control samplewithout dopamine.

To magnetize the PD-layer, iron oxide nanoparticles were incorporatedinto the coating. First, iron oxide NPs were formed by mixing Fe²⁺ withFe³⁺ ions, and magnetism was validated with a magnet. TEM images provideevidence of 10-20 nm sized crystals of iron oxide. These nanoparticleswere mixed with PD-coated NRs to form iron oxide-gold nanorodconjugates. Importantly, once these conjugates were purified by magnetand resuspended, the plasmon from the gold NR remained in suspension.TEM was performed and provided evidence of gold NRs conjugated to ironoxide nanoparticle clusters (FIG. 3).

To further functionalize the PD surface and enhance colloidal stability,PEG molecules containing functionalities reactive to PD were added tothe solutions. Importantly, addition of PEGs containing amines, thiols,catechols, and histidines (with imidazole functional group) intosuspensions of PD-primed NRs preserved the strong NIR SPRcharacteristics of the gold NRs after 18 hours of dopaminepolymerization and under centrifugation, as compared to controls withunreactive mPEG-NH—Ac (FIG. 4). Pegylated PD-coated NRs were imaged withEM (FIG. 5), which gave evidence of well-dispersed NRs. The red-shiftingof the longitudinal SPR of the NRs with PD-coating was preserved withpegylation (FIG. 6). Similar results were obtained with chitosan,pNIPAM, and peptoid coatings.

To further confirm the presence of PD, PEG, and silver on gold NRs, XPSwas performed. Spectra of CTAB-coated NRs contained a single C1s peakand a small O1s peak. Contrarily, PD-primed NRs spectra werecharacterized by a C1s shoulder at higher energies, and significantlyhigher O1s signal compared to CTAB counterparts. With regard to thepresence of PEG, compared to PD-coated NRs, all pegylated PD-coated NRswere characterized by higher C/N ratios, significant O1s signal, and twodistinct C1s peaks. PD-coated NRs incubated with silver and PEG hadsignificantly higher Ag/C ratios compared to nonmetalized counterparts,and significant O1s signal compared to CTAB and PD samples. A controlspectrum of NRs without PD coated with only PEG-SH gave significantlyhigher C/N ratios compared to any other samples due to the lack of N1ssignal, and O1s signal was pronounced compared to CTAB counterparts.

To conjugate the anti-EGFR antibody ERBITUX® (cetuximab) onto gold NRs,suspensions were initially reacted with dopamine in pH 8.5 for 30minutes, where red-shifting and broadening of plasmons occurred. Onceprimed with a thin layer of PD, ERBITUX® (cetuximab) was added to the NRsuspension, sonicated for 30 minutes, centrifuged and resuspended inwater. Addition of ERBITUX® (cetuximab) infusion to CTAB-coated NRsresulted in loss of the SPR in solution within 20 minutes. Whenbortezomib was added to PD-coated NRs and centrifuged without thepresence of PEG, permanent NR aggregation occurred. Therefore PEG wasadded after bortezomib in order to provide colloidal stability. Additionof ERBITUX® (cetuximab) after bortezomib also provided transientstability to the NRs for up to one hour.

To interrogate their cell-targeting capabilities, toxicity, and efficacyas optical theragnostic agents, NRs were incubated with OSCC15 cells invitro, and imaged with bright field microscopy, optical coherencetomography, and 2-photon confocal microscopy. Under bright field, largegold NR aggregates were present on the surface of cells incubated withCTAB-coated NRs. Even larger, micron-sized aggregates were present inPD-primed NR samples. Contrarily, when OSCC15 cells were incubated withpegylated NRs, the presence of NRs could not be detected after washing.To investigate the cellular toxicity of the functionalized NRs,CTAB-coated, PD-primed, and pegylated-PD-primed NRs were incubated withOSCC15 cells in vitro and stained with trypan blue. 100% of cellsincubated with CTAB-coated NRs for 30 minutes were stained with trypanblue. Contrarily, there was almost no trypan staining of cells incubatedwith either PD-primed NRs (0.12%) or pegylated PD-primed NRs (1.7%).

Cells were imaged with OCT. Compared to uncoated control cells, oralcancer cells coated with ERBITUX® (cetuximab)-conjugated silver-coatedgold nanorods provided bright signal, presumably from enhancedbackscattering in the red-portion of the spectrum. Cells were imagedwith a confocal microscope. Importantly, a differential interferencecontrast (DIC) image could be superimposed on a fluorescent imageexcited with a NIR laser tuned the SPR of the NRs. A spectrum of thevisible emission was acquired between 400 nm and 650 nm. Bright dotsassociated with NRs could be identified on cellular surfaces.

To interrogate their photothermal properties, NRs were embedded in analginate gel and irradiated with the Mai:Tai laser. Visible 2-photonexcited signal was detected using 2.5% power. The microscope was thenfocused to an area of high gold NR concentration, the power was turnedup to 5% and irradiated for 30 seconds. Gel morphological featurechanges occurred during irradiation, eventually giving rise to micronsized cavitation, presumably due to evaporation of some of the aqueousphase of the gel from extreme heating from the NRs. 2-photon excitedemission intensity from the gold nanorods coated in either CTAB or PD asa function of incident power was performed. Interestingly, at low power(0.2-1% max power) PD-coated NRs gave statistically significantlygreater signal. However, this trend changed and reversed at higherpowers (5-10% max power), with PD-coated NRs emitting statisticallysignificantly less signal.

Cellular toxicity experiments were performed to measure toxicity of thePD-coated NRs. In the first set of experiments, gold NRs coated inpolydopamine and PEG were incubated with OSCC15 cells. NRs with silveror bortezomib, or controls without additional materials. Controls showminimal toxicity at low concentrations and moderate death at highconcentrations. Addition of bortezomib or silver into the NR conjugatesignificantly increased its toxicity. In the second set of experiments,NRs were conjugated with bortezomib, and then capped with either PEG orthe anti-EGFR antibody ERBITUX® (cetuximab). Importantly, toxicity wassignificantly increased in the NR sample conjugated to both bortezomiband ERBITUX® (cetuximab) compared to all other conditions.

Targeted NP-mediated photothermal therapy was performed as described inthe methods. Cells incubated with NRs that were not irradiated did notshow significantly different toxicity compared to control. Cellsirradiated without the presence of nanorods did show increased deathcompared to control that was dependent on irradiation time. Importantly,cells incubated with ERBITUX® (cetuximab)-conjugated gold NRs that werealso irradiated showed statistically significant enhanced death comparedto irradiation alone.

Finally, magnetic targeting of conjugates described above, followed bylight irradiation, was performed on breast cancer cells in vitro. Themagnetic particles were moved to the area of interest using an exteriormagnet (magnetic targeting) and irradiated to provide photothermaltherapy to cancer cells. Synergistic killing was observed between theuse of the magnet and light irradiation (FIG. 7), which was attributedto the increase in NP concentration near cells after the use of themagnet. This increase in particle concentration near cells led to anincrease in heating sites upon light irradiation resulting in increasedcell death.

Example 2 Polydopamine-Enabled Surface Functionalization of GoldNanorods for Cancer Cell Targeted Imaging and Photothermal Therapy

In this example, we further describe the preparation and anticancerperformance of PD coated NIR-active gold NRs. Anti-EGFR antibodies wereconjugated to PD coated NRs and their use in targeted photothermaltherapy of cancer cells was demonstrated. Antibody functionalized NRswere significantly more toxic to cancer cells in vitro compared tountargeted NRs when irradiated with a broadband light source. Theexample demonstrates that PD-mediated surface modification is a usefulstrategy for conjugation of cancer-specific ligands to nanoparticlesurfaces, enabling the formation of biofunctional diagnostic andtherapeutic metal nanoparticles.

Light sensitive nanoparticles have the potential to be used foranticancer therapy if they can be targeted to surface receptors ofcancer cells. The aim of this example was to employ a novel biomimeticstrategy for presenting antibodies on surface plasmon resonant goldnanorods (NRs) to target growth factor receptors on cancer cell surfacesfor use in photothermal therapy.

A thin conformal coating of the biomimetic polymer polydopamine (PD) waspolymerized on the surface of gold NRs in basic aqueous conditions, andepidermal growth factor receptor antibodies (anti-EGFR) weresubsequently immobilized onto the biomimetic polymer layer. In vitrocell-binding affinity and near-infrared light activated cell death oforal and breast cancer cells incubated with anti-EGFR functionalized NRswere quantified by optical imaging.

A 5 nm thick PD coating was deposited onto gold NRs, and up to 400antibodies were subsequently bound per PD-coated NR. NRs functionalizedwith anti-EGFR antibodies were stable for at least 25 hours in serumcontaining media, and specifically bound to EGFR overexpressing cells.Illumination of NR targeted cells with near infrared light enhanced celldeath compared to dark controls and cells treated with antibody freeNRs.

The results demonstrate that PD facilitates the surfacefunctionalization of gold NRs with biomolecules, allowing cell targetingand photothermal killing of EGFR overexpressing cells. Polydopamine canpotentially be used with a large variety of nanoparticle platforms andtargeting ligands as a strategy for biofunctionalization of diagnosticand therapeutic nanoparticles.

Dopamine hydrochloride, cetyltrimetylammonium bromide (CTAB, 99%),sodium tetrachloroaurate(III) dihydrate (NaAuCl₄.2H₂O, 99%), sodiumborohydride (NaBH₄, 98%), ascorbic acid, glycine, and silver nitrate(AgNO₃, 99%) were obtained from Sigma-Aldrich (St. Louis, Mo.). The pHvalue of the glycine solution (0.2 M) was adjusted to 8.0 with 2M sodiumhydroxide before use. mPEG-SH (MW=5000) was purchased from Laysan Bio(Arab, Ala.). ALEXA FLUOR® 633 red fluorescent dye goat anti-mouse IgGantibody was purchased from Invitrogen (Carlbad, Calif.). Anti-EGFRantibody was obtained as a commercial infusion (ERBITUX® (cetuximab), 2mg/ml, ImClone LLC, Bristol-Myers Squibb) from the Robert H. LurieComprehensive Cancer Center pharmacy of Northwestern University(Chicago, Ill.). Ultrapure, deionized water (18.2 MΩ·cm) was used toprepare all of the aqueous solutions. OSCC15 cells were acquired fromthe lab of Dr. David Crowe at the University of Illinois-Chicago. MCF7and MDA-MB-231 cells were acquired from Dr. Dean Ho at NorthwesternUniversity.

Synthesis of Gold NRs.

The synthesis of CTAB-coated gold NRs (CTAB-NRs) was performed accordingto a slightly modified method previously described in the literature(Huang Yu-Fen et al., Journal of Colloid and Interface Science 301(2006):145-154). Briefly, CTAB aqueous solution (0.2 M, 5.0 mL, heatedto 30° C.) was mixed with 0.5 mM NaAuCl₄ (5.0 mL). Ice-cold 0.01 M NaBH₄(0.6 mL) was added to this solution and sonicated for 5 minutes to forma brownish-yellow seed solution. 50.0 mL of 0.2 M CTAB was then gentlymixed with 50.0 mL 1.0 mM NaAuCl₄ and 0.1 mL 0.1 M silver nitrate toform a growth solution. Ascorbic acid was added to the solution as amild reductant (78.8 mM, 0.7 mL), followed by addition of 120 μL of theseed solution. After 45 minutes, 100 mL of this gold NR solution wasmixed with 100 mL 0.2 M glycine (pH 8.0). This solution was allowed toreact overnight without stirring at ambient temperature.

Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES).

1 mL of the NR stock solution was centrifuged, supernatant removed, andthe pellet re-suspended in 500 μL 70% nitric acid. The sample wassonicated in a Branson 2510 sonicator in an ice water bath for 5 hoursto dissolve the NRs, after which 154 μL of the resulting solution wasadded to 4.846 mL pure water and the Au concentration determined in aVarian VISTA-MPX ICP-OES Spectrometer (Varian, Inc. Santa Clara, Calif.)using a calibration curve constructed from 0.1, 0.5, 1, 2, 5, and 10 ppmgold standards (dissolved in 2% nitric acid).

Preparation of PD Coated Gold NRs.

1 mL of CTAB NR suspension was centrifuged and the pellet resuspended in1.9 mL of a 516 μM dopamine solution buffered to pH 8.5 using 10 mM TRISbuffer. The NR suspension was sonicated for 30 minutes, centrifuged at9000 rpm for 10 minutes, and the supernatant was removed. PelletedPD-coated NRs (PD-NRs) were resuspended in 2 mL of ultrapure deionizedwater, and a UV-Vis-NIR spectrum was acquired to confirm the presence oflongitudinal and transverse SPR peaks. Additional centrifugation andremoval of supernatant was performed to remove unbound dopamine.

Preparation of PEG Grafted Gold NRs.

For comparison to antibody coated NRs, PEG grafted NRs (PEG-PD-NRs) wereprepared by suspending PD-NRs overnight in 1.7 mL 10 mM TRIS buffer (pH8.5) containing 5 μL of 0.4 mM mPEG-SH at 20° C. PEG grafted NRs wereisolated by centrifugation and resuspended in ultrapure deionized water.

Antibody Immobilization on Gold NRs.

PD coated gold NR suspension (9.1×10¹² NRs/L) was centrifuged andresuspended in 500 μL 10 mM TRIS buffer (pH 8.5). To immobilize theanti-EGFR antibody, 0-350 nM antibody was added to 500 μL PD-NRsuspensions and sonicated for 30 minutes. To remove unbound antibodiesfrom the suspension of PD-NRs functionalized with anti-EGFR antibodies(anti-EGFR-PD-NRs), the suspension was then centrifuged at 9000 rpm at23° C. for 10 minutes, supernatant decanted, and the pellet resuspendedin ultrapure water or DMEM. Anti-EGFR-PD-NRs were incubated with 10 nMfluorescent goat anti-mouse IgG secondary antibody, centrifuged,resuspended in 500 μL ultrapure water, and tested in a Synergy 4 HybridMulti-Mode Microplate Reader. To quantify antibody density, thefluorescent signal was normalized to NR background fluorescence, andcompared to a standard fluorescence curve from free IgG antibody.

Electron Microscopy (EM).

Pelleted NRs (54) were dropped on EM grids (Ted Pella, Redding, Calif.)and allowed to dry overnight in ambient conditions. Transmission EM(TEM), Z-contrast EM, secondary EM (SEM), and energy dispersive X-rayspectroscopy (EDS) spectral imaging were performed on a Hitachi HD-2300Ultra High Resolution FE-STEM (Hitachi City, Japan).

Optical Spectroscopy.

A Hitachi (Hitachi City, Japan) U-2010 Spectrophotometer was used toacquire optical spectra in a two-beam geometry. To match the NRsuspension, 10 mM TRIS buffer, ultrapure deionized water, or DMEM wasused for the reference beam. Spectral scans were performed over the200-1000 nm range of wavelengths in the UV-Visible-NIR region of thespectrum. A deuterium lamp was used for the 200-340 nm UV rangeillumination and a halogen lamp was used for the visible and NIRillumination. Spectral resolution was 1 nm.

In Vitro Cell Imaging with NRs.

5×10⁵ oral squamous cell carcinoma 15 (OSCC15), MDA-MB-231 (breast) andMCF7 (breast) cancer cells were grown in tissue culture plates for 3days. OSCC15 cells were grown in high glucose DMEM (10% FBS, 1%gentamycin), MCF7 cells were grown in high glucose DMEM both with andwithout insulin (10% FBS, 1% pen/strep), and MDA-MB-231 cells were grownin RPMI-1640 media (10% FBS, 1% pen/strep). 2 mL of trypsin was added toconfluent plates of OSCC15 cells, cells were removed, and 400 μL wasadded to 2 mL of DMEM high glucose media. Cells were centrifuged at 1500rpm for 5 minutes, supernatant was removed, and 2 mL more media wasadded. NR suspensions were added to the cells and incubated for 30minutes. Cells were centrifuged at 1500 rpm for 5 minutes, supernatantwas removed, 2 mL of media was added, and finally cells were centrifugedand plated onto glass optical microscopy slides. Bright field imageswere acquired in a Leica DMRX microscope. To quantify binding, 5×10⁴MDA-MB-231 cells were grown in 12-well plates and imaged in an opticalcoherence tomography (OCT) system after incubation with anti-EGFR-PD-NRsfor 1 hour. OCT intensity between 750 and 850 nm localized to individualcells was quantified and plotted as a function of antibodyconcentration.

NR-Mediated Photothermal Therapy.

MDA-MB-231 and OSCC15 cells were cultured in 6-well and 12-well platesand allowed to grow to confluence. Cells were incubated withanti-EGFR-PD-NRs (0.1-20 pM) for 30 minutes-3 hours, washed twice withmedia, and irradiated with 50 mW NKT photonics SUPERK™ Versa lasersource for 5, 10, or 15 minutes; spot size was 1 mm. 1 μL 4 mM calceinand 1 μL 4 mM ethedium bromide was added to each well, and cells wereincubated for 15 minutes. Fluorescence microscopy was performed on aLeica DMIRB microscope, with a 250 W maximum Hg arc lamp, and a QIClickdetector (QImaging). For each irradiated spot, both calcein-stainedcells and ethidium bromide-stained cells were counted, and the % viablecells was calculated (n=1-3 spots).

X-Ray Photoelectron Spectroscopy (XPS).

NR samples were centrifuged, and pellets were deposited onto siliconoxide surfaces and allowed to dry. An Omicron (Taunusstein, Germany)XPS/ESCA Probe was used to acquire spectra. A survey scan over 0-1100 eVbinding energy range with 0.5 eV resolution was performed. Higher 0.04eV resolution spectra were acquired on the identified Au 4f_(7/2) and4f_(5/2), C 1s, O 1s, and N 1s peaks. The binding energy spectral rangeswere 82.5-90.5 eV for Au, 283.5-289.02 eV for C, 530.5-536.5 for O, and395.0-405.0 eV for N. Spectra were calibrated to the C—C peak, locatedat 284.5 eV.

Quantitative OCT Cell Imaging.

5×10⁴ OSCC15, M DA-MB-231, and MCF7 cells were incubated withanti-EGFR-PD-NRs in media at 37° C. for 1 hour, washed with media twice,and imaged in an optical coherence tomography (OCT) imaging system (FIG.8). A low coherence laser beam output from a supercontinuum source(SUPERK™ Versa, NKT photonics) was coupled into a single mode fiber andcollimated into an open space Michelson interferometer. A beam splitterdivided the beam into sample and reference arms and a well correctedmicroscopic objective created a 5 mW focused illumination with effectiveNA=0.04. A galvo mirror guided the beam before the objective to realizethe B-scan. The reference arm included a reflecting mirror, a neutraldensity filter, and a quartz plate for dispersion compensation. Thereflected beams from two arms were recombined by the beam splitter andcoupled into a spectrometer through a single mode fiber.

Inside the spectrometer, the interfered beam was collimated by an f=30mm lens and directed to a holographic diffraction grating (1200grooves/mm). A commercially available lens (Nikon f=135 mm) focused thedispersed beam on a 2048 pixel line scan camera (e2v) to record thespectrum from 650 nm to 820 nm resulting in an axial resolution of ˜2 μmin air. Two function generators (Agilent) were synchronized to drive thegalvo scanning mirror and provide exposure trigger to the camera. Theframe rate was 5 fps to maximize the signal to noise ratio. Cells wereidentified in the image, and the average pixel intensity per cellbetween 750-850 nm was quantified to determine NR density.

Quantification of IgG Antibody Density on Gold NRs.

Due to the difficulties of quantifying the amount of EGFR antibody boundto the NR surface, the following approach was used to provide anestimate of bound antibody. 0-350 nM goat anti-mouse IgG antibodyconjugated with ALEXA FLUOR® 633 red fluorescent dye (Invitrogen) wasincubated with PD-NRs in 10 mM TRIS buffer (pH 8.5) for 30 minutes in500 μL aliquots. Samples were centrifuged, supernatant was removed, andpellets were resuspended in identical 500 μL volumes. The fluorescentintensities of the supernatant solutions were compared to a standardcurve in a Synergy 4 Hybrid Multi-Mode Microplate Reader to quantify theconcentration of unbound antibodies.

To quantify the concentration of bound antibody, the fluorescentintensities of the resuspended pellets were normalized to the backgroundintensity from PD-NRs without antibody addition and compared to astandard curve. The number of antibodies per NR was determined bycomparing the concentration of bound antibody to the NR concentration(calculated from the gold atom concentration from ICP-OES and goldnanoparticle size from TEM assuming a right circular cylinder shape asdescribed in main text).

After centrifugation and separation of the NRs from the supernatantsolution, the ratio of immobilized to free antibody was 2.6 for PD-NRs,compared to 0.12 for CTAB-NRs (FIG. 9a ), corresponding to a 22-foldincrease in antibody immobilization on PD-coated NRs compared toCTAB-coated NRs. Further, the number of antibodies per NR was tuned byvarying the concentration of antibody added to a constant PD-NRconcentration, up to a surface density of 350 per NR (FIG. 9b ).

Results.

In this example, a general strategy was used to immobilize antibodiesonto gold NR surfaces through an intermediate PD layer (FIG. 10). First,high yield (>95%) CTAB-NRs were synthesized using established protocols.The apexes of the transverse and more intense longitudinal extinctionpeaks of CTAB-NRs were located at 520 nm and 783 nm, respectively, andwere stable during storage in excess CTAB at room temperature for atleast 6 months. CTAB-NRs were imaged by TEM and had an average length of62±6 nm and width of 17±3 nm (n=123) (FIG. 11). 0.294±0.013 mg/L of goldwas detected in the NR suspension treated with nitric acid described inthe methods. Taking this concentration, the density of gold, andassuming a right circular cylinder shape, the gold NR concentration inthe initial stock suspension was determined to be 1.81×10¹³ NRs/L (30.1pM).

PD deposition was accomplished by dispersion of CTAB-NRs in an alkalinedopamine solution, upon which spontaneous deposition of PD onto NRsaccompanied by displacement of the CTAB ligand was observed. UV-Visextinction spectra acquired during this process revealed a linearred-shift over time (FIG. 12a ), corresponding to a PD coating of 5 nmthickness as observed by secondary electron microscopy (FIG. 12b ).

To further confirm the presence of PD on the surface of gold NRs, XPSwas performed (FIG. 13). In contrast to the single C1s peak observedfrom CTAB-NRs, high resolution C1s spectra of PD-NRs were characterizedby a peak centered at 284.5 along with a significant shoulder towardhigher energies representative of C—O and C—N bonds in the PD.

To provide clinically relevant anticancer functionality, anti-EGFRantibodies were immobilized onto PD-NRs at pH 8.5 for 30 minutes.Red-shifting and broadening of the longitudinal SPR occurred duringconjugation (FIG. 14a ). To further confirm the presence of the antibodyon the gold NR, anti-EGFR-PD-NRs were stained with a secondaryanti-mouse IgG antibody, and fluorescent signal representative of anantibody monolayer (^(˜)400 antibodies/NR) on the PD coating wasdetected. Stability of the anti-EGFR-PD-NRs was tested in DMEM mediaover the span of 24 hours, with no statistical loss in SPR intensityobserved (FIG. 14b ).

To explore EGFR targeting, anti-EGFR-PD-NRs were incubated with twocancer cell lines characterized by high EGFR expression, OSCC15 oralcancer cells[65] and MDA-MB-231 breast cancer cells (Fitzpatrick, 1984).Optical microscopy revealed that anti-EGFR-PD-NRs were visiblyinteracting with cells, whereas NRs were not visible on cells treatedwith PEG-PD-NRs in identical conditions (FIGS. 15a and b ). Further, aconcentration dependent increase in NIR light intensity (750 nm-850 nm)localized to cellular structures was observed in MDA-MB-231 cellsincubated with anti-EGFR-PD-NRs (FIG. 15c ), with a 4.1 fold increase inlight intensity observed at an antibody concentration of 5.7 nM ([NR]=14pM). No increase in intensity was observed in low-EGFR expressing MCF7breast cancer cells incubated with anti-EGFR-PD-NRs (data not shown).

Next, we demonstrated photothermal therapy of OSCC15 cells targeted withanti-EGFR-PD-NRs (FIGS. 16 and 17). In control experiments, no toxicityof cells was observed immediately after irradiation in the absence ofNRs (FIG. 16a ), or in cells incubated with anti-EGFR-PD-NRs withoutirradiation (FIG. 16b ). Whereas cells incubated with 9.92 pM PEG-PD-NRsand then irradiated maintained 91% viability (FIG. 16c ), viability ofcells incubated with the same concentration of anti-EGFR-PD-NRs and thenirradiated decreased to 24% (FIG. 16d ). Thus, cells targeted withanti-EGFR-PD-NRs and irradiated with light were killed more efficientlythan any other treatment (FIG. 17a ).

NR-mediated photothermal therapy was also performed on MDA-MB-231 breastcancer cells, which exhibit overexpression of EGFR. Like OSCC15 cells,MDA-MB-231 cells treated with anti-EGFR-PD-NRs but not irradiatedmaintained high viability at all time points tested in this study,whereas irradiation significantly decreased viability in aNR-concentration dependent manner (FIG. 17b ). After 5 minutes ofirradiation, cells not treated with NRs were 79% viable; in the sameconditions, cells incubated with anti-EGFR-PD-NRs were between 37% and70% viable depending on the NR concentration. Further, longer incubationtimes with anti-EGFR-PD-NRs provided enhanced toxicity when coupled withirradiation (FIG. 17c ).

Discussion.

Gold NRs have shown promise as contrast agents and photothermaltherapeutic agents in vitro and in vivo. However, a versatile chemicalapproach is needed to couple the optically functional metalnanoparticles with a broad range of biologically specific molecules inphysiological environments to fully realize their biomedical potential.Catecholamine molecular adhesives, inspired by the protein glues ofmussels that adhere to wet, chemically heterogeneous surfaces in diverseaqueous environments, can be exploited to functionalize metalnanoparticle surfaces for biomedical applications. PD is perhaps thesimplest form of a mussel mimetic coating in terms of ease of use andversatility, depositing spontaneously as a thin conformal coating onsurfaces by taking advantage of a rich repertoire of chemicalinteractions with surfaces. The thickness of PD coatings as well astheir deposition rate can be easily tailored through depositionconditions such as pH and dopamine concentration.

PD deposition on the gold NR surface was indicated by a red-shift of thelongitudinal SPR (FIG. 10a ), XPS analysis showing a C1s shoulderrepresentative of C—O and C—N bonds in the PD coating (FIG. 13), andsecondary EM images revealing a 5 nm thick PD layer surrounding gold NRs(FIG. 12b ). A multivalent interaction occurs between PD and the metalNR surface, likely including pi electron, electrostatic, and metalcoordination interactions, giving rise to a robust cohesive coating thatmimics the molecular adhesives evolved in mussels that thrive inturbulent sea environments with similar characteristics to high ionicstrength, high flow in vivo conditions.

PD coatings further serve as a platform or ‘primer’ onto which furthersurface modifications can be performed. In this study, PD was used inthis way to provide a versatile chemical interface for conjugation ofantibodies and other biomolecules onto the surface of NIR-active goldNRs for targeting cancer cells. When coupled to metal nanoparticles,antibodies offer complementary biological functions like specificbinding to human cell surface receptors associated with cancerphenotypes such as EGFR, the human epidermal growth factor receptor 2(HER2), glucose transporters like GLUT1 that are upregulated underglycolysis, and mucin receptors such as MUC1.

To quantitatively characterize the general immobilization of antibodiesonto PD-NRs, fluorescently-tagged IgG antibodies were incubated withPD-NRs in alkaline conditions. A 22-fold increase in immobilizedantibody was observed compared to CTAB-NRs (FIG. 9a ), illustrating theadvantage of using PD for biomolecule conjugation to surfaces. Thenumber of antibodies per NR could be controlled between 8 and 350 (FIG.9b ), the latter number corresponding to an antibody monolayerimmobilized onto a 5 nm thick PD layer surrounding a 62 by 17 nm goldNR.

To create an anticancer NR using the biomimetic PD approach, anti-EGFRantibodies were immobilized onto the PD layer. Immobilization ofanti-EGFR antibody onto gold NRs produced a red-shift and broadening ofthe longitudinal and transverse plasmon bands of the gold NR (FIG. 14a). Anti-EGFR-PD-NRs were stable in serum-containing medium for at least25 hours (FIG. 14b ), avoiding nonspecific interactions and NRaggregation and facilitating specific targeting to EGFR-expressing cells(FIG. 15) where they provided a light activated therapeutic response(FIGS. 16 and 17).

Anti-EGFR-PD-NRs added to cell culture media strongly interacted withEGFR-expressing cells (FIG. 15), producing a 4-fold enhancement of theOCT signal in the NIR range (FIG. 15c ) due to the backscattering fromgold NRs bound to cells. OCT signal increases were detected as low as0.3 nM antibody, significantly lower than the dissociation constant(K_(d)) values for free antibody of 4.54 nM, which could be caused bymultivalent enhanced binding through multiple antibodies on a single NR.In contrast, OCT intensity from MCF7 cells lacking high EGFR expressionwas not enhanced by incubation with anti-EGFR-PD-NRs at any of theconcentrations tested, implying that the increase in intensity from theMDA-MB-231 cells upon incubation with anti-EGFR-PD-NRs was due tobinding of NRs to cells through a specific antibody-receptorinteraction.

In the future, quantitative EGFR-targeted spectroscopic imaging withanti-EGFR-PD-NRs could be used to help identify high risk,EGFR-expressing phenotypes with bright field microscopy of ex vivobiopsies or OCT of tumors in vivo. Due to their sub-100 nm particlesize, targeting specificity, and PD interface that decreases in vivotoxicity and immunological response, anti-EGFR-PD-NRs should be capableof intravenous in vivo administration in an effort to increase antibodydelivery efficiency to tumor sites through the enhanced permeability andretention (EPR) effect that occurs in leaky tumor vasculature.

Once bound to cancer cells, irradiation with light transforms NRs intopotent therapeutic agents, providing a second therapeutic mechanism inaddition to the current antibody-based EGFR inhibition. Our resultsindicate that light irradiation of anti-EGFR-PD-NRs targeted to oral orbreast cancer cells provided enhanced therapeutic efficacy compared tocontrol treatments. The observed toxicity arising from NIR irradiationof anti-EGFR-PD-NRs bound to OSCC15 and MDA-MB-231 cells is likely dueto direct thermal damage caused by cavitation upon irradiation, asheating of gold NRs can produce extreme local temperatures at the NRsurface and to yield bulk temperature increases in the range of 10 to50° C. Alternatively, toxicity may arise from secondary effectsassociated with hyperthermia such as calcium influx-induced membraneblebbing. Further studies will be necessary to elucidate the mechanismof cell death produced by light irradiation of anti-EGFR-PD-NRs.

The responses observed in both oral and breast cancer cells demonstratethe clinical potential of anti-EGFR-PD-NRs toward EGFR-specificpathologies, however the strategy is broadly applicable to any antibodyand could in the future be used to target other cancer-related cellsurface receptors, such as HER2, GLUT1, and MUC1. Furthermore, theversatility of the PD surface modification strategy facilitates highlytailored surface modifications that include multiple biological ligands,passivating polymers like PEG, and other targeting ligands such aspeptides and DNA aptamers.

Finally, we note that our approach could prove to be a useful adjunct toexisting surgical oncology practices. For example, we envision that NIRirradiation of NRs could be used as a complement to current tumorexcision techniques to decrease the likelihood of recurrence. EmployingNRs as opposed to spherical gold nanoparticles shifts the relevantwavelengths into the NIR range, which penetrates far deeper into tissuethan visible light, allowing in principle noninvasive activation of NRsfor treatment of currently inoperable tumors. Since therapeutic efficacywas observed even at the lowest concentration tested (62.5 pM antibody,0.21 pM NR), systemic in vivo administration of NRs could providesufficient dose to tumor sites to observe a light-induced therapeuticresponse.

PD offers a versatile chemical interface for coupling of biologicalmolecules with metal nanoparticles, as illustrated by the synthesis ofPD-functionalized gold NRs conjugated with anti-EGFR antibody. Theanti-EGFR-PD-NRs were stable in serum containing media and selectivelybound to cells expressing EGFR. Although the anti-EGFR-PD-NRs were nottoxic to cells in the absence of light, significant photo-inducedtoxicity of breast and oral cancer cells was observed upon exposure toNIR light. In the future, this biomimetic strategy can be expanded toinclude other functional nanomaterials like superparamagnetic ironoxide, and other targeting and therapeutic moieties such as smallmolecule drugs and other cell-surface targeting antibodies, in order toform multifunctional agents for specific diagnosis and combinationtherapy for complex resistant diseases such as heterogeneous cancers andantibiotic resistant bacteria.

Example 3 Plasmonic Heating Enhances Antibacterial Effect ofSilver-Coated Gold Nanorods

In this example, polydopamine (PD) is used to coat gold nanorod (NR)surfaces and deposit silver in order to tune SPRs and provideantibacterial functionality. Antibacterial antibodies are reacted to PDsurfaces through catechol redox reactions to providebiologically-specific targeting to bacterial cell walls. Thesemultifunctional biomimetic metal NRs target both gram-negative E. coliand gram-positive S. epidermidis, providing contrast in optical imaging.Finally, light irradiation provides a potent therapeutic response tobacteria targeted with metal NRs, providing multiple mechanisms ofaction that includes cell-targeted photothermal heating and silver-basedtoxicity. The example demonstrates that catecholamine-based interfaceshave the potential to form a broad range of biotargeted metal NPs forthe diagnosis and treatment of antibiotic resistant bacterial infectionsand other diseases.

In this example, we use a catecholamine-based approach to control theSPR and biological functionality of colloidal metal NPs with shape andcompositional control for multifunctional photothermal treatment ofbacterial cells. PD is used to combine a NIR-active gold NR, silver, andantibacterial antibodies to form multicomponent antibacterialphotothermal agents (FIG. 18). PD adheres strongly to gold NR surfacesby forming a conformal cross-linked interface, immobilizes silver ontogold NRs in a controlled manner, and covalently reacts to antibodies toprovide biofunctionalization. When functionalized with the properantibody and irradiated with light, these metal NRs efficiently killedboth gram-positive Staphylococcus epidermidis (S. epidermidis) andgram-negative Escherichia coli (E. coli). More broadly, the biomimeticchemistry of PD offers a versatility that may prove useful in theformation of multifunctional antibacterial metal NPs that providephotothermal therapeutic treatment in the ongoing arms race betweenmicrobes and man.

Dopamine hydrochloride, cetyltrimetylammonium bromide (CTAB, 99%),sodium tetrachloroaurate(III) dihydrate (NaAuCl₄.2H₂O, 99%), sodiumborohydride (NaBH₄, 98%), ascorbic acid, glycine, and silver nitrate(AgNO₃, 99%) were obtained from Sigma-Aldrich (St. Louis, Mo.). The pHof 0.2 M glycine solution was adjusted to 8.0 with 2M sodium hydroxidebefore use. Heterobifunctional PEG (methoxy-PEG-SH, mPEG-SH, MW=2 kDa)was purchased from Laysan Bio (Arab, Ala.). Antibody against endotoxinof gram negative bacteria, and antibody against lipoteichoic acid ofgram-positive bacteria were purchased as a solution (0.1 mg/ml) fromMyBioSource (San Diego, Calif.). SYTO® 9 green fluorescent nucleic acidstain and propidium iodide were purchased from Invitrogen (Grand Island,N.Y.). Staphylococcus epidermidis (RP62A) and Escherichia coli (J5mutant, 43745) bacteria were purchased from ATCC (Manassas, Va.).

Gold NR Synthesis.

Gold NRs with longitudinal SPRs in the NIR portion of theelectromagnetic spectrum were synthesized in surfactant-containing watersolutions according to previously described protocols (Y. F. Huang etal., Journal of Colloid and Interface Science 301 (2006): 145-154) andsummarized here. Aqueous CTAB solution (0.2 M, 5.0 mL, heated to 30° C.)was mixed with 0.5 mM NaAuCl₄ (5.0 mL). Ice-cold 0.01 M NaBH₄ (0.6 mL)was added to this solution and sonicated for 5 minutes to form abrownish-yellow seed solution. 50.0 mL of 0.2 M CTAB was then gentlymixed with 50.0 mL 1.0 mM NaAuCl₄ and 0.1 mL 0.1 M silver nitrate toform a growth solution. Ascorbic acid was added to the solution as amild reductant (78.8 mM, 0.7 mL), followed by addition of 120 μL of theseed solution. After 45 minutes, 100 mL of this gold NR solution wasmixed with 100 mL 0.2 M glycine (pH 8.0). This solution was allowed toreact overnight without stirring at ambient temperature.

PD-Functionalized Antibacterial NR Synthesis.

PD was deposited onto gold NRs. 500 μL of gold NR suspension wascentrifuged and resuspended in 1 mL of 10 mM TRIS buffer (pH 8.5).Dopamine hydrochloride was added to a final concentration of 0.555-1.11mM and sonicated for 30 minutes to form PD-NRs. To incorporate silverinto the PD-layer surrounding gold NRs, 0-300 μM AgNO₃ in ultrapure DIwater was added under stirring, and samples were sonicated for 10minutes. Samples were centrifuged at 9000 rpm for 10 minutes, andsupernatant solution was decanted. To immobilize the antibodies, 12.5 μLof the 0.1 mg/ml antibody solution was added to NR suspensions andsonicated for 30 minutes, and then 10 μL 1 mg/ml mPEG-SH (pH 8.5) wasadded and sonicated for 30 minutes to backfill the PD layer withpassivating polymers. Six distinct formulations of the PD-NRs, with andwithout silver (Ag), and with and without one of the two antibodies (Ab)were used in subsequent studies (described as PEG-NRs, PEG-Ag-NRs,Ab-NRs, and Ab-Ag-NRs; see FIG. 19 for a schematic representation).

Optical Spectroscopy.

A Hitachi (Hitachi City, Japan) U-2010 Spectrophotometer was used toacquire optical spectra in a two-beam geometry. 10 mM TRIS buffer (pH8.5) was used for the reference beam. Spectral scans were performed at aresolution of 1 nm over the 200-1000 nm range of wavelengths in theUV-Visible-NIR region of the spectrum.

Electron Microscopy.

Pelleted NRs (54) were deposited on EM grids (Ted Pella, Redding,Calif.) and allowed to air dry. Transmission EM (TEM), Z-contrast EM(ZCEM), secondary EM (SEM), and energy dispersive X-ray spectroscopy(EDS) spectral imaging were performed on a Hitachi HD-2300 Ultra HighResolution FE-STEM (Hitachi City, Japan). The beam was operated at 200kV.

Quantitative Photothermal Heating Experiments.

NR samples were centrifuged and resuspended in 50 μL ultrapure deionizedultrapure water. Samples were irradiated with a 50 mW NKT photonicsSUPERK™ Versa laser source (650 nm-850 nm) with a 1 mm spot size for 10minutes. NR suspension temperature was monitored with a Luxtron 1652Industrial Fluoroptic Thermometer (Lambda Photometrics; Hertfordshire,UK) with a fiber optic thermocouple STF (Shanghai Thermostat Factory)probe designed for harsh environments.

Bacterial Assays.

S. epidermidis and E. coli were grown overnight in Tryptic soy andLuria-Bertani growth media, respectively, under shaking at 37° C. 1 mLof the bacterial suspension was centrifuged at 4600 rpm at 4° C. for 5minutes, the supernatant decanted, cell pellets were resuspended in 3 mL0.85% NaCl solution, and the process was repeated 3 times. 1 mL of thecell suspension (10⁹ CFU/mL) was added to 40 μL PEG-NR, PEG-Ag-NR,Ab-NR, or Ab-Ag-NR pellets, incubated under shaking for 20 minutes at37° C., and then centrifuged at 2000 rpm at 4° C. for 5 minutes.Supernatant was removed, and the cell pellets were resuspended in 50 μLsterile 0.85% NaCl solution. 5-10 μL were placed onto a glass side andimaged with an optical coherence tomography (OCT) system. Photothermaltreatments were performed on 5 μL of the cell suspension placed in a 600μL eppendorf tube, which were irradiated with 50 mW NKT photonicsSUPERK™ Versa laser source (650 nm-850 nm) with a 1 mm spot size for 10minutes. Cells were stained with SYTO® 9 green fluorescent nucleic acidstain and propidium iodide (Invitrogen) according to manufacturer'sspecifications, and imaged with an epifluorescent microscope. Cellviability was quantified by counting individual numbers of live and deadcells with ImageJ software (6 fields of view per condition, ^(˜)100cells per field of view).

Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES).

2 mL of PD-coated nanorod (PD-NR) suspension was centrifuged. 100 μL ofthe supernatant was added to 200 μL 70% nitric acid and sonicated for 4hours at 22° C. in a Branson 2510 sonicator. The remaining supernatantwas removed, and the pellet was resuspended in 50 μL. 5.5 μL was addedto 200 μL 70% nitric acid and sonicated for 4 hours. Pure water wasadded to bring the total volume to 4 mL samples. Ag concentration wasdetermined in a Varian VISTA-MPX ICP-OES Spectrometer (Varian, Inc.Santa Clara, Calif.) using a calibration curve constructed from 0.1,0.5, 1, 2, 5, and 10 ppm silver standards (dissolved in 2% nitric acid).Gold NR concentration was quantified by methods described previously(see Example 2).

X-Ray Photelectron Spectroscopy (XPS).

NR samples were centrifuged, and pellets were deposited onto siliconoxide surfaces and allowed to dry. An Omicron (Taunusstein, Germany)XPS/ESCA Probe was used to acquire spectra. A survey scan over 0-1100 eVbinding energy range with 0.5 eV resolution was performed. Higher 0.04eV resolution spectra were acquired on the identified Au 4f_(7/2) and4f_(5/2), Ag 3d, C 1s, O 1s, and N 1s peaks. The binding energy spectralranges were 82.5-90.5 eV for Au, 364.0-380.0 eV for Ag, 283.5-289.02 eVfor C, 530.5-536.5 for O, and 395.0-405.0 eV for N. Spectra werecalibrated to the C—C peak, located at 284.5 eV.

Results.

Synthesized gold NRs were characterized by strong longitudinal SPRscentered near 800 nm and less intense transverse SPRs near 520 nm.Deposition of PD onto gold NR surfaces caused a slight red-shift in thelongitudinal SPR (FIG. 20a ), and the coating was visible undersecondary electron microscopy (FIG. 20b ). Within seconds of silveraddition, a pronounced color change occurred in the suspension. Theobserved colors stabilized within 10 minutes, which included red,yellow, green, purple, and orange (FIG. 21a ), from low to high silverconcentration respectively. This color change was accompanied by apronounced increase in intensity, sharpening, and blue-shift of thelongitudinal SPRs (FIG. 21b ). Addition of 50, 100, 200, and 300 μMsilver nitrate to a PD-NR suspension with an initial longitudinal SPRextinction peak centered at 804 nm shifted the peak to 693 nm, 629 nm,565 nm, and 531 nm, respectively. The blue-shift observation wasindependent of the initial wavelength of the longitudinal SPR (data notshown). A strong optical backscattering peak that was red-shiftedcompared to overall extinction was observed from these metal NRs (FIG.21c ).

Electron microscopy was performed to confirm the deposition of silveronto PD-NRs. Gold NR core-silver shell NP morphologies were evidentunder TEM (FIG. 22a ) and ZCEM (FIG. 22b ), and average coatingthicknesses between 1 and 8 nm were tuned by the concentration of silveradded. Gold and silver were spatially identified on a single NP with EDS(FIG. 23), revealing a gold rod core (red) surrounded by a silver shell(teal), as evidenced by the increase in the Ag/Au ratio in the EDSspectra, which was confirmed by ICP-OES (FIG. 24). A significantlyhigher Ag 3d signal was observed in XPS spectra of samples incubatedwith silver compared to nonmetalized counterparts (FIG. 25).

The photothermal properties of the NR suspensions were characterizedupon irradiation, and substantial heating occurred in NR suspensionscompared to water controls (FIG. 26). PEG-NR suspensions increased from20.6° C. to 24.2° C. within 1 minute, rising to 41.9° C. in 5 minutes,and reached a steady state condition of 44° C. after 8 minutes ofirradiation. Addition of silver into the PD layer moderately decreasedthe temperature increase compared to PD-NRs without silverincorporation. These NR suspensions increased from 20.6° C. to 22.1° C.in the first minute of irradiation, rose to 38.5° C. after 5 minutes,and reached a steady state condition of 40° C. in 8 minutes. Watercontrols irradiated identically only increased to 21° C. in the firstminute, reached 24° C. in 5 minutes, and did not significantly increaseover the next five minutes of irradiation.

To provide bacterial strain specificity to PD-NRs, antibodies thattarget lipoteichoic acid in gram-positive bacterial cell walls orendotoxin on gram-negative cell walls were immobilized onto the PDlayer. Red-shifts of the NR SPRs occurred upon initial antibodyfunctionalization, which matched previously reported results, afterwhich no statistical shift in SPRs occurred in 0.85% salt solutions over4 hours (FIG. 27). 87% and 54% of the SPR intensity of Ab-Ag-NRs andAb-NRs preserved, respectively. A 7 nm shift was detected in Ab-NR SPRsover 24 hours, but no shift was detected in Ab-Ag-NR SPRs over the sametime period.

Biomimetic antibacterial metal NRs were incubated with gram-negative E.coli and gram-positive S. epidermidis bacterial cells and characterizedwith OCT (FIG. 28). After incubation with antibody-functionalized NRsand centrifugation to remove unbound NRs, bacterial pellets were visiblydarkened; cell pellets incubated with PEG-functionalized NR controlswere significantly less intensely stained. Under OCT, both E. coli andS. epidermidis cell suspensions exhibited increased brightness andcontrast after incubation with antibody-functionalized NRs as comparedto PEG-functionalized NRs, and silver deposition onto NRs furtherincreased both the brightness and contrast of the OCT images (FIG. 28).Features from the tail of the SPR were detected from cell pellets,particularly with S. Epidermidis (FIG. 29a ), implying co-localizationof cells and NRs.

Photothermal therapy was performed successfully on gram-positive S.epidermidis and gram-negative E. coli (FIGS. 30, 31, and 32). Withregard to S. epidermidis, multiple components were necessary to providekilling. Incubation with PEG-NRs, PEG-Ag-NRs, and Ab-NRs, followed byirradiation with 50 mW broadband light did not produce therapeuticresponses, yielding cell viabilities of 90%, 91%, and 94%, respectively,not significantly different than untreated controls. However, strongsynergistic therapeutic responses were observed between Ab-Ag-NRs andlight irradiation (FIG. 30). More specifically, only NRs coated insilver and functionalized with antibodies specific to lipoteichoic acidthat were also irradiated with light provided robust S. epidermidiskilling. With this treatment, cell viability was reduced to 10%.

The synergistic effects from silver, antibody, and light were lessobvious but still observed in the case of E. coli (FIG. 31). PEG-NRswere moderately toxic to E. coli cells (73% viability), and theirviability was reduced to 63% when irradiated with light. Incubation withPEG-Ag-NRs reduced E. coli viability to 58%, and addition of irradiationprovided a robust effect, reducing viability to 15%. NRs functionalizedwith antibodies (Ab-NRs) that bind to endotoxins aggregated into cellclusters, and cell viability was reduced to 46% when irradiated withlight. Addition of silver into the PD layer surrounding the NRs enhancedthe toxicity of the irradiation-induced effect, killing 92% of thebacteria in solution (8% viability).

Discussion.

Photothermal therapeutic agents composed of gold NRs coated with PD,silver, and antibacterial antibodies were synthesized (FIG. 18). InExamples 1 and 2, PD was deposited onto gold NRs to provide a versatilecatecholamine chemical surface for further functionalization. In thisexample, these PD-NRs (FIG. 20) were employed as antibacterial agents byincorporating silver and antibodies into the PD primer layer to targetbacterial cell surfaces for silver-based antibacterial photothermaltherapy.

In order to provide antibacterial properties to the NIR-active gold NRs,silver was deposited onto NRs. Silver binds DNA, interferes withenzymes, and binds to cell surface molecules, making it amultifunctional antimicrobial that has had therapeutic success againstotherwise antibiotic resistant bacteria. The antibacterial coating wasdeposited by the addition of silver nitrate into basic PD-NRsuspensions. We hypothesize that upon addition of silver nitrate, thecatechols in the PD layer, which reduce gold and silver ions in basicsolutions, reduce silver ions into metal silver embedded in a PD matrixsurrounding gold NRs. This was confirmed by the successful detection ofsilver on gold NRs with EM (FIG. 22), EDS spectral imaging (FIG. 23),and ICP-OES (FIG. 24), as well as the detection of metallic silver inXPS (FIG. 25). The thickness of the silver coatings, between 1 and 8 nm,was easily controlled by varying the amount of silver nitrate added tothe NR solution.

Silver deposition on gold NRs also caused a distinct suspension colorchange associated with SPR blue-shifting and sharpening (FIGS. 21 and23). By controlling the thickness of the silver coating, thelongitudinal SPR extinction peak wavelength could be tuned between 520nm and 860 nm. This SPR tuning also implies that the silver-containingPD layer has conductive properties, and that silver doping provides anavenue to tune the band-gap properties of melanin-like semiconducting PDinterfaces. This SPR control is useful in solving the broader challengeof matching the optical properties of targeted metal NPs with lightsources for imaging and photothermal therapy. Tissue penetration is amajor limitation of in vivo optical imaging techniques that can bemaximized by using NIR light, however higher resolution imaging oftissue surfaces can be acquired with shorter wavelength visible light.Importantly, the metal PD-NRs described here can be assembled such thattheir optical properties are optimized for either application. Peaksharpening was also observed by silver shell deposition, associated withplasmonic focusing, an effect that increases their potential as contrastagents.

Increased scattering also occurs at the silver-gold interface of theAg-NRs (FIG. 21c ), and can be detected in optical diagnostic imagingtechniques like dark field microscopy and OCT. Indeed the increasedbrightness and SPR spectral features observed in OCT images of cellsamples incubated with Ab-Ag-NRs (FIGS. 28 and 29) is due to thebackscattering (FIG. 21c ) from the metal NRs bound to cells. Silverdeposition also increases the magnitude of light extinction per NR (FIG.21b ). Taken together, the addition of silver to the NRs makes themantibacterial, plasmonically tunable, and more efficient detection andtreatment agents. However, in order for photothermal and silvertreatments to work efficaciously the NR must be in close proximity withthe bacteria.

To adhere metal NRs directly to the bacterial cell walls, antibacterialantibodies specific to components in the membrane can be immobilized toPD-NR surfaces by reaction under mildly basic conditions. To targetgram-negative cells, antibodies for endotoxin were conjugated to NRs;for gram-positive cells, antibodies specific to lipoteichoic acid wereimmobilized. SPR red-shifts were detected upon functionalization in bothPD-NRs and Ag-NRs, indicating a thicker coating on NRs, results similarto those described in the previous examples. It is hypothesized thatamines in the antibodies covalently react with the quinones of the PDlayer. With the addition of antibodies along with PEG, the NRs werestable in salt solutions over a period of 4 hours (FIG. 27), with SPRsof Ab-Ag-NRs not shifting over 24 hours, indicating their stability insaline environments.

OCT imaging confirmed antibody-functionalized NR targeting to bacterialcells. After incubation with antibody-functionalized NRs and washing,cell suspensions of both E. coli and S. epidermidis were significantlybrighter compared to control cells incubated with PEG-NRs (FIG. 28).This results from the increased number of NRs present in the sample, dueto enhanced binding of NRs to bacterial cells, providing brightbackscattering contrast in OCT. Additionally, due to the increasedscattering from the gold-silver interface, Ab-Ag-NRs were significantlybrighter under OCT compared to Ab-NRs. This increased brightness andcontrast upon binding can be used for detection of specific strains ofbacteria with particular membrane components with high sensitivity andsignal-to-noise ratio. While two specific antibacterial antibodies forendotoxin and lipoteichoic acid were used in this study, otherantibodies and smaller targeting molecules like peptides and antibodyfragments can be integrated into the described PD-based strategy.

Once targeted to bacterial cells, NRs can be irradiated with light toproduce a potent therapeutic response. The SPR of the metal NRs causeshigh absorption of light energy, leading to substantial heating (FIG.26). In this study, substantial bulk temperature rises between 20-25° C.from baseline were detected upon irradiation of NRs, which correspond toeven higher local temperature increases from NR surfaces. Further, PD issimilar in structure to melanin, a natural photopigment evolved toprotect organisms from light damage by converting light energy to heat,which may enhance the conversion of light to heat. Since the NRs aretargeted to the cell surface, the extreme heating upon irradiationlocally disrupts cellular membranes, resulting in effects that can rangefrom moderate swelling to pressure induced cavitation from bubblesformed by water evaporation and metal NP explosion.

Synergistic therapeutic effects occurred between the presence of silverand light irradiation in the bacterial cell viability assays. Sincesilver actually decreased NR photothermal potential (FIG. 26), it ishypothesized the enhanced toxicity is due to release of silver uponirradiation. Potentially, as the temperature rises, the PD layersurrounding the NR can become damaged through denaturation ordestabilized through other effects such as vibrations or local waterevaporation, which can produce silver release in ionic or particulateform. Once released, silver provides multiple therapeutic effects,including binding to DNA, respiratory enzymes, and cell surfacemolecules and receptors.

Gram-negative E. coli cells were efficiently killed by irradiation afterincubation with metal NRs (FIG. 31), and synergistic responses wereobserved between the multiple components of the therapy. Light-activatedtoxicity was detected even when incubated with PEG-NRs, a phenomenonsignificantly enhanced with addition of silver into the system,presumably due to silver release upon irradiation. NRs targeted withantibodies and irradiated were more toxic compared to PEG controls dueto the binding of the NRs to the cell membrane by the conjugatedantibody. NRs coated in silver and functionalized with antibodiesprovided greater killing when coupled with irradiation than any otherformulation. This implies that binding the particles to the cell surfacewith antibodies and irradiating them with light, to simultaneously causemembrane damage and release silver, provides multifunctionalphotothermal therapy.

Interestingly, S. epidermidis was evidently more resistant to lighttreatment in the presence of NRs (FIG. 30). Distinct from E. coli, thepresence of the NR, silver, antibody, and the use of irradiation wereall necessary to efficiently kill S. epidermidis cells in solution. Itis hypothesized that the thick peptidoglycan layer in the cell walls ofgram-positive bacteria like S. epidermidis, which is not present ingram-negative counterparts like E. coli, protects against the extremeheating that occurs from cell-wall-bound NRs upon irradiation. However,by combining a NIR active metal NP, silver, and antibacterial antibodieswith PD, the multifunctional antibacterial agents bind to lipoteichoicacid embedded in the peptidoglycan layer with antibodies, thenphotothermally damage the cell membrane while simultaneously releasingsilver when irradiated with light to kill the cells.

Metal NPs have SPR material properties that can be harnessed for avariety of biomedical applications when their surfaces arebiofunctionalized, including photothermal treatment of bacterial cells.Natural bioadhesives of the marine mussel have evolved to adhere to anymaterial in harsh, salty environments, and catecholamine molecularlayers inspired by mussel adhesive proteins have the flexible chemicalrepertoire necessary to provide a robust multifunctional interfacebetween metal NP surfaces and organic molecules like PEG and antibodies,which are a central weapon in the human immune system. By coupling theirfunctionality with the electromagnetic properties of metal NPs throughbiomimetic adhesives, hybrid biometallic nanomaterials can be engineeredto treat resistant diseases like cancer and bacterial infections withnovel, individualized therapies that integrate NP-enhanced photothermaltherapy with cell surface targeting.

The invention is not limited to the embodiments set forth herein forillustration, but includes everything that is within the scope of theclaims. Furthermore, all references cited herein are hereby incorporatedby reference in their entirety and for all purposes as if fully setforth herein.

1. A nanoparticle comprising: (a) a metallic core having a length alongeach axis of from 1 to 100 nanometers; and (b) a coating disposed on atleast part of the surface of the metallic core, wherein the coatingcomprises polydopamine.
 2. The nanoparticle of claim 1, wherein themetallic core is a nanorod having a substantially cylindrical shape. 3.The nanoparticle of claim 1, wherein the coating is disposed on theentire surface of the metallic core.
 4. The nanoparticle of claim 1,wherein the metallic core is selected from the group consisting of gold,silver or iron oxide.
 5. The nanoparticle of claim 4, wherein themetallic core consists essentially of gold.
 6. The nanoparticle of claim1, wherein the coating further comprises silver, iron oxide, or amixture thereof.
 7. The nanoparticle of claim 1, further comprising oneor more antibodies, polyethylene glycol, functionalized polyethyleneglycol, or a mixture thereof bound to the coating.
 8. The nanoparticleof claim 7, wherein the antibody is an anti-cancer cell surface receptorantibody or an anti-bacterial surface antibody.
 9. The nanoparticle ofclaim 1, further comprising a polymer, a polysaccharide, asugar-containing peptoid, a pharmaceutical agent, or a mixture thereofbound to the coating.
 10. The nanoparticle of claim 9, wherein thepharmaceutical agent is an anti-cancer agent or an anti-microbial agent.11. A method of making the nanoparticle of claim 1, comprisingcontacting a metallic core having a length along each axis of from 1 to100 nanometers with an alkaline solution comprising dopamine, whereby apolydopamine coating is formed on the surface of the metallic core. 12.The method of claim 11, wherein the metallic core is a nanorod having asubstantially cylindrical shape that consists essentially of gold.
 13. Amethod for treating cancer comprising administering to a patient havingcancer cells one or more nanoparticles of claim 8, wherein the metalliccore consists essentially of gold and wherein the antibody is ananti-cancer cell surface receptor antibody, whereby the one or morenanoparticles target the cancer cells and the cancer is effectivelytreated.
 14. The method of claim 13, wherein the anti-cancer cellsurface antibody is an anti-epithelial growth factor receptor (EGFR)antibody.
 15. The method of claim 13, wherein the one or morenanoparticles further comprise an additional anti-cancer agent bound tothe coating.
 16. The method of claim 15, wherein the anti-cancer agentis a proteasome inhibitor.
 17. The method of claim 13, furthercomprising the step of exposing the nanoparticles to light.
 18. A methodfor treating a bacterial infection comprising administering to a patientinfected with bacteria one or more nanoparticles of claim 8, wherein themetallic core consists essentially of gold and wherein the antibody isan anti-bacterial surface antibody, whereby the one or morenanoparticles target the bacteria and the bacterial infection iseffectively treated.
 19. The method of claim 18, wherein theanti-bacterial surface antibody is an anti-lipoteichoic acid antibody oran anti-endotoxin antibody.
 20. The method of claim 18, wherein thecoating of the one or more nanoparticles further comprises silver. 21.The method of claim 20, further comprising the step of exposing thenanoparticles to light.
 22. A method for imaging cancer or bacterialcells comprising: (a) contacting cancer or bacterial cells with one ormore nanoparticles of claim 8, wherein the metallic core consistsessentially of gold and wherein the antibody is an anti-cancer cellsurface receptor antibody or an anti-bacterial surface antibody, wherebythe one or more nanoparticles target the cancer or bacterial cells; and(b) detecting the location of the one or more nanoparticles.
 23. Themethod of claim 22, wherein the step of detecting the location of theone or more nanoparticles is performed using bright field microscopy,optical coherence tomography, or 2-photon confocal microscopy.
 24. Themethod of claim 22, wherein the nanoparticle coating further comprisesiron oxide, and wherein the step of detecting the location of the one ormore nanoparticles is performed using magnetic-based imaging.
 25. Amethod for treating cancer, the method comprising administering to apatient having cancer cells one or more nanoparticles of claim 8,wherein the metallic core consists essentially of gold and wherein theantibody is an anti-cancer cell surface receptor antibody, and exposingthe nanoparticles to light, whereby the one or more nanoparticles targetthe cancer cells and the cancer is effectively treated.
 26. A method fortreating a bacterial infection comprising administering to a patientinfected with bacteria one or more nanoparticles of claim 8, wherein themetallic core consists essentially of gold and herein the antibody is ananti-bacterial surface antibody, and exposing the nanoparticles tolight, whereby the one or more nanoparticles target the bacteria and thebacterial infection is effectively treated.